The present invention relates to the general technical field of hot beverage machines and in particular electric coffee makers, in which the preparation of the beverages obtained by lixiviation of a ground product, such as ground coffee, in a hot liquid, generally water, serving as a solvent.
The present invention is more particularly directed to an electric coffee maker which includes water heating means, a water reservoir, a water distribution chamber having at least one water distribution outlet opening, a tube for conducting water upwardly from the reservoir to the distribution chamber, a filter holder supported below the water distribution chamber, a water recycling conduit connecting the water distribution chamber to the reservoir, and a valve for controlling the blocking or unblocking of the water distribution outlet opening so as to permit, when the outlet opening is blocked, recycling of the water via the recycling conduit.
Coffee makers provided with a water recycling system have been developed in order to prevent water which is not sufficiently hot, particularly at the start of an operating cycle, from being brought into contact with the ground product, i.e. ground coffee, in which event the result would be the production of a beverage not having its most desired temperature. In effect, in coffee makers which do not have a recycling system, it has been found that the final temperature of the beverage in the serving container, or carafe, is substantially lower than in machines provided with such a system. In addition, it is recognized that the optimum extraction of soluble components from the ground coffee is obtained when the temperature of the water passing through the ground product is held constant and is sufficiently high for the entire duration of the operating cycle of the coffee maker.
German Patent C-2932053 describes an electric coffee maker of the filter type which includes a reservoir, water heating means, and a water distribution chamber situated above a filter holder and provided with a control valve for controlling the opening and closing of an outlet opening of the water distribution chamber, the outlet opening being located above the filter holder. The machine described includes a system for recycling water which has not achieved the desired temperature. The recycling system consists of a recycling conduit connecting the water distribution chamber to the reservoir.
The control valve includes a bimetallic element in contact with water in the water distribution chamber. The bimetallic element is deflected to open the water outlet opening when the water has achieved a sufficiently high temperature. During operation of the coffee maker, water arriving in the water distribution chamber is continually recycled to the reservoir via the conduit for as long as the desired temperature has not been attained.
Known coffee makers designed according to this principle permit, to a certain extent, the attainment of a satisfactory beverage temperature and one can consider that the extraction of essences from the ground coffee is equally effected under acceptable conditions. However, it has been found that the total duration of an operating cycle, and in particular that of the water preheating phase, is considered unacceptably long in view of the heat losses occurring at the level of the conduits for recycling and raising the water. It has equally been noted that during the course of operation of such machines, the water is subjected to an excessive degree of evaporation over its return path from the reservoir toward the heater, producing characteristic noise which is considered objectionable by users.